Trailers are often called upon to transport hazardous materials, such as flamable liquids, gasoline, pesticide, strong acids and alkalines, poisonous liquids or perishable goods such as milk or other perishable refrigerated substances. At present, draft vehicles must be specially made in order to accommodate trailers, since the fifth wheel height of the draft vehicle must be the same as the kingpin height of the trailer if they are to be used together. In an effort to allow any draft vehicle with sufficient power to be used with a trailer with different fifth wheel height, various attempts have been made to equip draft vehicles with adjustable fifth wheel heights. Two such attempts are Van Langen U.S. Pat. No. 2,515,575 and Gurton et al U.S. Pat. No. 2,590,962. Both are examples of vehicles with hydraulically adjustable fifth wheels. Each of the patents cited above are designed to do different function than the present invention and differ from each other as well. Van Langen uses a tiltably mounted fifth wheel adjusted by a hydraulic cylinder piston rod. When fluid is pumped into the front of the cylinder, the fifth wheel is raised until its movement is halted by a bell crank arrangement. The drawback to the Van Langen invention is that while such a vehicle so equipped may fit any trailer skid plate height, it cannot haul the vehicle for any considerable distance. It is designed merely to raise and lower the trailer so that on inclined areas, the fifth wheel height can be adjusted so that when lifting the trailer, the trailer remains level. It is limited as a long range moving device because of the fore and aft forces associated with draft vehicle-trailer motion. Upon examination of the Van Langen device it can be seen that while Van Langen did contemplate long range hauling, he did not contemplate such hauling in the elevated position because, owing to the construction of the Van Langen device, the strain associated with forward or backward movement would cause undue wear and strain upon the hydraulic shift means. In order for the Van Langen device to haul trailers for long distance, the fifth wheel is first raised to the desired height, and when the draft vehicle and trailer were properly connected, the fifth wheel is lowered to its normal position for enabling the entire assembly to be transported. Thus it can be seen that at times the trailer draft vehicle side view would appear as an angle less than the desired 180.degree. norm. Such an arrangement would make driving different and likely more dangerous than a driver would normally expect. Indeed, in military situations, with four different fifth wheel heights, the driver would have to be accustomed to potentially many different tractor trailer arrangements. The present invention avoids such shortcomings by providing a trailer which is equipped to accommodate any of several different draft vehicles. By adjusting the trailer skid pad, the trailer can be towed by any sufficiently powered draft vehicle without altering the horizontal profile from the desired 180.degree. norm and so eliminate the driving hazards associated with Van Langen. Also, Van Langen's use of hydraulic cylinder is expensive to install, control and maintain. The present invention's structure mode of adjustment, ease of adjustment and simplicity of construction contrast sharply with the expense and complexity associated with a hydraulic device.
Gurton et al U.S. Pat. No. 2,590,962 also uses hydraulic means to adjust to accommodate trailers with fifth wheel heights. Gurton et al is novel in that neither the draft vehicle or the trailer are altered in any way, rather a third vehicle, a detachable dolly trailer, is equipped hydraulically and is interposed between the trailer and the draft vehicle. In this manner, the dolly's fifth wheel is adjusted to the desired position. The dolly is attached to the draft vehicle and the entire arrangement is ready to travel any distance. Although an advancement over Van Langen U.S. Pat. No. 2,515,575, in that a trailer could be hauled over long distances by a draft vehicle of different fifth wheel height, the dolly in the adjusted position has some of the same disadvantages as Van Langen. Among these is the hydraulic system utilized in Gurton et al which is relatively expensive to install and maintain and is fairly complex in construction and design. In addition to the disadvantages cited above, Gurton et al contemplates the maintainence of an additional fleet of vehicles, namely the dollys. Many if not most companies today can ill afford to have business capital tied up in such equipment. The present invention is simple, inexpensive and can be used in most trailers, give some modifications. Thus, the present invention contributes to less dead heading and a quicker turn around time for any trailer so equipped when it reaches its destination. Finally, flexibility of the trailers in any given fleet is enhanced by each trailer being able to be used with any suitably powered draft vehicle, regardless of fifth wheel heights.